Size-dependent strain-engineered nanostructures in MoS₂monolayer investigated by atomic force microscopy

Abstract

The strain has been employed for controlled modification of electronical and mechanical properties of two-dimensional (2D) materials. However, the thermal strain-engineered behaviors of the CVD-grown MoS 2 have not been systematically explored. Here, we investigated the strain-induced structure and properties of CVD-grown triangular MoS 2 flakes by several advanced atomic force microscopy. Two different kinds of flakes with sharp-corner or vein-like nanostructures are experimentally discovered due to the size-dependent strain behaviors. The critical size of these two kinds of flakes can be roughly estimated at∼17 μm. Within the small flakes, the sharp-corner regions show specific strain-modified properties due to the suffering of large tensile strain. While in the large MoS 2 flakes, the complicated vein-like nanoripple structures were formed due to the interface slipping process under the larger tensile strain. Our work not only demonstrates the size-specific strain behaviors of MoS 2 flakes but also sheds light on the artificial design and preparation of strain-engineered nanostructures for the devices based on the 2D materials.

Twist angle-dependent work functions in CVD-grown twisted bilayer graphene probed by Kelvin probe force microscopy

“…Many electrical SPM techniques, such as scanning microwave impedance microscopy, electrostatic force microscopy (EFM), C-AFM, and KPFM, have been used to investigate the local electrical properties of 2D materials. 32,[42][43][44][45] KPFM is an atomic force microscopy (AFM) technique for spatially mapping and studying the surface topography and local work function variations simultaneously under ambient conditions. 37,40,46 The spatial resolution in the KPFM mode was ∼700 nm and the voltage resolution was ∼1.8 mV.…”

Recent advances in defect-engineered molybdenum sulfides for catalytic applications

“…The generation of strain depends on force effects such as substrate-induced strain, 19 lattice mismatch-induced strain, 41 and shaping-induced strain. 42 For instance, Li and coworkers applied strain to the MoS 2 monolayer based on a nanostructured substrate. 19 Specifically, the CVD-grown MoS 2 monolayer was wet-transferred onto a SiO 2 nanocone substrate pre-patterned using nanosphere lithography.…”

Visualization of Strain-Engineered Nanopattern in Center-Confined Mesoscopic WS2 Monolayer Flakes

“…Diverse methods have been proposed for introducing strain in 2D materials, including the bending of films on elastic substrates, − the stretching of films using atomic force microscopy (AFM) probes, − thermal expansion mismatch, − and so on. With the help of AFM, our group recently has focused on strain-induced nanostructures in real space and their specific physical properties, including ripples and wrinkles. − …”

“…The magnitude of the tensile thermal strain within the WS 2 /SiO 2 flakes not only depends on the TEC mismatch but also the size of the flakes . For a relatively small sample (<50 μm)which has less strainstrain domains with triple symmetry have been observed in these layers. ,− Although many studies on strained 2D materials have been conducted, the mechanical behavior of WS 2 monolayers at the submicron scale has not been fully understood.…”